Why Waste Them, Blowes Ragstone

QUARRY BY PRODUCTS WHY WASTE THEM?
A CASE STUDY
Ragstone Extraction in Kent:
Hermitage Quarry
Joan Blows BSc MSc DIC CGeol
Independent Engineering Geologist,
Visiting Lecturer, Faculty of Engineering and Science
KENTISH RAGSTONE
typically a hard, sandy, glauconitic
limestone
[interbedded with softer, poorly
cemented sandstones - Hassock ]
British Geological Survey (BGS)
KENTISH RAGSTONE
-occurs in the Hythe Formation
Hythe Formation
Ragstone quarries (blue squares), as listed in the
records of the British Geological Survey (BGS)
Geological map produced by the BGS
KENTISH RAGSTONE a very, very brief introduction
• Quarried since Roman times.
• Valued as a building stone.
• Nearest source of durable dimension stone to
London.
• Ready Navigation links developed from wharfs at
Maidstone along River Medway
River Thames
London.
• Much used in Mediaeval times.
• Heyday of high quality stone in 15th C.
• Great decline in its use from 17th - brick more
fashionable- and from mid 19th C railways allowed
use of more easily worked freestone such as Bath
Stone.
Kent Conservation Officers set up
Ragstone Working Party
•
concern over diminishing availability
of Ragstone building stone
•
Key Strategic Resource
of Building Stone in the South East of
England
Just a few examples of the historic use
of Ragstone
12th C Rochester Castle
15th C Westgate
Towers Canterbury
16th C Upnor Castle
Historic River Wall Maidstone
Some different types of use of Ragstone
In 1990 Hermitage (Ragstone) Quarry
opened
Main Products from the quarrying
operations at Hermitage:
Coarse Aggregate (from 40mm - 5mm)
Riprap and Gabion Stone
Building Stone (for walling and dimension stone)
Stone (75-40mm) for drainage and bulk fill
purposes
Road sub base material - Type 1
RAGSTONE
(Light grey bands)
HASSOCK
(Buff coloured bands)
Initially, Hermitage Quarry produced the Ragstone
products listed above
plus Hassock, sold as bulk fill, Class 1A.
Introduction of the Aggregates Levy Tax in 2002
affected the economics of selling Hassock as bulk fill
material.
excess Hassock then became an unwanted byproduct of Ragstone processing and was landfilled.
The total proportion of ‘waste’ material from Hythe
beds originally about 70%
Quarry waste comprises 29% of waste
produced in UK
DEFRA 2007
National planning policy objective is
to move the treatment of waste “up
the hierarchy”
At Hermitage Quarry New production system set up, with a new
wash plant.
Not only allowing separation of the
‘Ragstone feed’ from the ‘Hassock feed’
but new washing system increases the
quality & quantity of the aggregates
produced.
A high performance processing plant =>
70+ products
14 And 10mm Aggregates made
using Hassock
Hermitage Quarry Washing Plant
Hermitage (Ragstone) Quarry
Now the unwanted products
(‘waste’) from the Ragstone
production
essentially reduced to the silt
stream
and reducing the quarry waste
to about 10%
The values of of this Ragstone resource
was recognised and in 2013, planning
permission was granted for a new phase
(25Yrs) of Ragstone extraction at Hermitage
Quarry – “The Western End”
However, further extraction results in the
production of more ’waste’ materials
Production of building stone from
Hermitage Quarry
Primary saw installed
in quarry
Cut blocks ready for next
stage of processing
Flow chart of processes
at Hermitage Quarry
Can the proportion of ‘Hermitage
waste’ (quarry fines)
be reduced even further??
Contaminated Land Remediation
and Waste Management
(Greenwich University) Research
Programmes
Accelerated Carbonate Technology
(ACT) trials carried on quarry fines
from Hermitage Quarry.
And Table 5.4
Figure 5.3.8/
Hassock Sand
Hassock Silt
Particle Size Distribution of Gallagher Sands
Percentage Passing
100
90
80
70
60
50
40
30
20
10
0
Hassock Sand
Ragstone Sand
Aperture Size (mm)
Particle Size Distribution of Gallagher Silts
100
90
Percentage Retained
80
70
60
Hassock Silt
Ragstone Silt
50
40
30
20
10
0
0.01
0.1
1
10
Particle Size (um)
100
1000
a
b
Final pelletised product; a: 30% ash pellets, b:
50% ash pellets
The future?
Thank you
and thanks to Gallagher Aggregates Ltd
& Dr Peter Gunning, University of Greenwich